Morgan Ivey is a graduate student at Clemson University working on my M.S. of Hydrogeology.
Influence of Methane Inhibitors and High Molecular Mass Electron Donors on Chlorinated Solvent Biodegradation
Chlorinated solvent bioremediation encompasses a number of combined microbial and chemical reactions that oxidize or reduce the contaminant(s) of concern. In the case of trichloroethylene (TCE), many approaches rely on adding electron donors to stimulate chlororespiration, in which cells gain energy to grow by sequentially reducing TCE to ethene.
In recent years, the idea that TCE could be reduced by inhibiting methane production to stimulate dechlorination has been put into practice by vendors. The theory is that if methane production is inhibited, electrons will be redirected to chlorinated solvent reduction for complete dechlorination. However, if methanogenesis is inhibited, then microbial activity that is key in reducing chlorinated solvents may, or may not, occur. Additionally, adding carbon substrates to the subsurface rarely targets a single microbial population, and several microbial groups respond to electron donor amendment.
The purpose of this research is to evaluate the influence of methane inhibitors on chlorinated solvents by using electron donors in various concentrations. Electron donors include plant-based essential oils, lactate, and statins. The work will demonstrate that inhibiting methanogenesis alone may not expedite dechlorination, and the broader impacts on the microbial community that are central to reducing TCE are larger than this single reaction. It is anticipated that using electron donors at near stoichiometric concentrations will help control methanogenesis while facilitating complete dechlorination.
Data suggest that experiments containing high molecular mass electron donors may be more effective when paired with a methane inhibitor than when applied alone, specifically for lactate and emulsified vegetable oils. However, the addition of some amendments intended to be methane inhibitors may be ineffective at controlling methane production, and in some cases methanogenesis increased due to the other materials present with statins (e.g. yeast). One statin used appears to not be inhibiting methane production at all, but two plant-based essential oils could be effective at controlling methanogenesis during dechlorination. Although the vendors market these with added electron donors, each of the materials acts as an electron donor on its own. The statin may be less effective because of a misreported statin content in the red yeast rice carrier. Future analysis will determine whether the product contains a high enough percentage of statin compounds to be effective at controlling methanogenesis.